Optical data recording disc with protrusion between clamping area and center hole

ABSTRACT

A disc-shaped optical data recording medium has a signal recording layer for reading and/or writing data using light, and a 10 μm to 200 μm thick transparent protective layer disposed over the signal recording layer. The optical data recording medium includes a protrusion projecting from a surface of the transparent protective layer on a light-incidence surface side to which light is emitted to the signal recording layer. The protrusion is disposed in an area between a center hole and a clamping area where the optical data recording medium is held when reading and/or writing data in the signal recording layer.

This application is a divisional application of U.S. application Ser.No. 11/365,819, filed Mar. 2, 2006, which is a divisional application ofU.S. application Ser. No. 10/655,135, filed Sep. 5, 2003, now U.S. Pat.No. 7,065,776.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disc-shaped optical data recordingmedium having a signal recording layer for recording and/or playinginformation by emitting a light beam thereto, and a transparentprotective layer 10 μm to 200 μm thick disposed over the signalrecording layer. The invention also relates to a method formanufacturing this optical data recording medium, and to a method forclamping the optical data recording medium.

2. Description of Related Art

Optical discs are known and widely used as a high capacity data storagemedium for high density recording and playback of information using alaser beam. These optical discs are broadly categorized as read-only,incrementally writable (multisession), and rewritable. Typical ofread-only discs are Compact Discs (CDs) storing audio content and LaserDiscs storing video content such as movies. Both incrementally writable(multisession) and rewritable media are widely used in the computerindustry, for example, for storing text documents and still image files.

These optical discs typically have a data layer disposed to one mainside of a 1.2 mm thick transparent substrate. A protective overcoat isthen applied to the data layer, or a protective disc identical to thetransparent substrate is bonded by adhesive to the data layer. See, forexample, Japanese Laid-Open Patent Publication No. 2001-093193,paragraph [0015] and FIG. 1, and Japanese Laid-open Patent PublicationNo. 2002-042376, paragraph [0019] and FIG. 1.

Development and introduction of Digital Versatile Discs (DVD), a highcapacity optical disc medium, has made it practical for even end-usersto record moving picture content (such as movies and video) togetherwith audio to an optical disc. High density media such as DVD have beenachieved by using a shorter wavelength laser and an objective lens witha large numeric aperture (NA). However, shortening the beam wavelengthand increasing the NA also reduce the tolerance for tilt, theinclination of the disc to the direction of laser beam emission.

Tolerance for tilt can be improved by using a thinner substrate. WithDVD media this means, for example, using a 0.6 mm thick substrateassuming a 650 nm laser and 0.60 NA. Because a 0.6 mm thick substrate ismechanically weak and would thus increase tilt, DVD discs have two suchsubstrates bonded together with the data recording surfaces on theinside between the substrates.

By using this laminated structure a transparent reflective layer of goldor silicon, for example, is formed on the data recording surface of oneof the two substrates, and a conventional reflective layer of aluminum,for example, is formed on the data recording surface of the othersubstrate. The substrates are then bonded together with these datarecording surfaces facing each other on the inside, resulting in asingle-sided, double-layer DVD that can be read from one side of thedisc, that is, from the side of the substrate having the transparentreflective layer over the data recording layer. Rewritable DVD mediawith a similar double-layer construction are also available, but thedata recording surface in this case is a rewritable thin-film recordinglayer instead of a metal mirror layer.

Using a blue-purple laser with an approximately 400 nm wavelength hasalso been proposed as a way to achieve even higher recording densities.One method uses an approximately 0.1 mm thick transparent protectivelayer on the read/write side and forms an ultrafine laser spot using anapproximately 0.85 NA lens for signal reading and/or writing. Thetransparent layer can be formed with the following two methods.

(A) Bonding a transparent substrate slightly less than 0.1 mm thick tothe signal surface side of a 1.1 mm thick signal substrate usingadhesive.

(B) Coating the signal surface side of a 1.1 mm thick signal substratewith an approximately 0.1 mm thick transparent resin layer.

In method (A) a polycarbonate sheet manufactured by casting, forexample, is used as the transparent substrate. Thickness variation insuch cast sheets is minimal at approximately +/−1 μm. The thickness ofthe adhesive used to bond this polycarbonate sheet to the signalsubstrate is also thin and can be easily formed to a uniform thickness.As a result, a transparent protective layer with uniform thickness canbe formed on the recording/playback side of the disc.

With method (B) it is difficult to form a uniformly thick coatingbecause of the thickness of the transparent resin, but a low cost, highdensity optical disc can be achieved because it is not necessary to usesheets manufactured in a high cost casting process.

SUMMARY OF THE INVENTION

A problem with high density optical discs is that the surface of thetransparent protective layer is easily scratched, and scratches caneasily cause a loss of servo control. Increasing the mechanical strengthof the transparent protective layer itself increases the film thickness,and is not suited for high density recording. It is therefore difficultto protect the surface from scratching while keeping the transparentprotective layer thin.

The data transfer rate during recording and playback is higher with highdensity optical discs than conventional CD and DVD media, and the disctherefore spins faster. Imbalances in the shape and weight of the discrelative to the spindle hole can therefore increase the load on therotating spindle (motor).

In addition, high speed rotation of these high density optical discsalso requires higher disc clamping force than CD and DVD discs.

The present invention is therefore directed to solving these threeproblems, and an object of the invention is to provide an optical datarecording medium having surface protrusions for protecting thetransparent protective layer and reducing the load on the motor duringdisc rotation, and enabling higher disc clamping force to be applied tothe optical data recording medium.

To achieve the above objects an optical data recording medium with asignal recording layer for reading and/or writing data using light, anda 10 μm to 200 μm thick transparent protective layer disposed over thesignal recording layer, comprises a protrusion projecting from thesurface of the transparent protective layer on the light-incidencesurface side to which light is emitted to the signal recording layer inan area between a center hole and a clamping area where the optical datarecording medium is held when reading and/or writing data in the signalrecording layer.

Because this protrusion is on the inside circumference side of theclamping area, the protrusion will not interfere (collide) with theoptical head. Furthermore, when the optical data recording medium isplaced on a flat surface with the transparent protective layer sidefacing the flat surface, the protrusion keeps the transparent protectivelayer off the flat surface and thereby prevents scratching thetransparent protective layer.

The load imposed on the rotating spindle (motor) caused by a weightimbalance in the protrusion is also reduced because the protrusion islocated near the center spindle hole.

The protrusion is preferably disposed separated at least 0.1 mm in theradial direction from an outside edge of the center hole. Thisconfiguration prevents the protrusion from interfering with the centercone used to hold the optical data recording medium at the spindle holein the disc recording and playback drive, and thereby enables stableclamping of the optical data recording medium.

In another aspect of the invention a disc-shaped optical data recordingmedium with a signal recording layer for reading and/or writing datausing light, and a 10 μm to 200 μm thick transparent protective layerdisposed over the signal recording layer, is characterized by having aclamping area on the outside of the center hole in the radial directionfor holding the optical data recording medium when reading or recordingdata in the signal recording layer; a signal area on the outside of theclamping area in the radial direction for recording or reading data inthe signal recording layer; and a protrusion projecting from the surfaceof the transparent protective layer in an area disposed between theclamping area and signal area on the light-incidence side of the signalrecording layer to which light is emitted for reading and/or writinginformation.

When this optical data recording medium is placed on flat surface withthe transparent protective layer thereof facing the flat surface, theproximity of the protrusion to the signal area keeps the transparentprotective layer separated from the flat surface and thereby providesexcellent protection for the transparent protective layer.

Preferably, the protrusion is disposed to an area within 2 mm to theoutside in the radial direction from the outside circumference edge ofthe clamping area.

Interference between the protrusion and the optical head is thus furtherprevented because the protrusion is sufficiently separated from thesignal area.

A disc-shaped optical data recording medium having a signal recordinglayer for reading and/or writing data using light, and a 10 μm to 200 μmthick transparent protective layer disposed over the signal recordinglayer, according to a further aspect of the invention is characterizedby a clamping area on the outside of the center hole in the radialdirection for holding the optical data recording medium when reading orrecording the signal recording layer; a signal area on the outside ofthe clamping area in the radial direction for recording or reading datain the signal recording layer; and a protrusion projecting from thesurface of the transparent protective layer in the clamping area on thelight-incidence side of the signal recording layer to which light isemitted for reading and/or writing information.

This optical data recording medium is clamped on both sides of theprotrusion in the clamping area. There is therefore no interference(collision) with the optical head, and the transparent protective layerwill not be scratched when the disc is placed on a flat surface with thetransparent protective layer facing said flat surface because theprotrusion disposed to the same side of the disc keeps the transparentprotective layer raised above the flat surface.

Further, greater clamping force can be applied and the disc can be spunstably, assuring good signal quality. The load imposed on the rotatingspindle (motor) caused by a weight imbalance in the protrusion is alsoreduced because the protrusion is located near the center spindle hole.

Preferably, the protrusion projects to a height of 0.05 mm to 0.5 mmfrom the surface of the transparent protective layer. The transparentprotective layer will therefore not be scratched when the disc is placedon a flat surface with the transparent protective layer facing the flatsurface because the protrusion projects sufficiently above the discsurface on the same side to keep the transparent protective layer fromcontacting the flat surface. Scratch-prevention and cost are furtherimproved if the protrusion height is further preferably 0.1 mm to 0.3 mmfrom the surface of the transparent protective layer.

Yet further preferably, the wavelength of light for recording or readinginformation in the signal recording layer is 410 nm or less so that asmall beam spot enabling high density recording and playback can beachieved.

Another aspect of the present invention is a manufacturing method for adisc-shaped optical data recording medium having a signal recordinglayer for reading and/or writing data using light, a 10 μm to 200 μmthick transparent protective layer disposed over the signal recordinglayer, and a protrusion projecting from the surface of the transparentprotective layer on the light-incidence surface side to which light isemitted to the signal recording layer. This manufacturing method hassteps for: preparing a first die with a cavity corresponding to theprotrusion, and a second die corresponding to the first die; disposingand closing the first die and second die together; injecting resinbetween the first die and second die; curing the resin to form a resinmolding having the protrusion; and opening the first die and second die,and removing the cured resin molding.

In another manufacturing method for a disc-shaped optical data recordingmedium having a signal recording layer for reading and/or writing datausing light, a 10 μm to 200 μm thick transparent protective layerdisposed over the signal recording layer, and a protrusion projectingfrom the surface of the transparent protective layer on thelight-incidence surface side to which light is emitted to the signalrecording layer, a substrate for the optical data recording medium isformed by injection molding using a die having a cavity corresponding tothe protrusion, and the protrusion is simultaneously formed on thesubstrate.

These manufacturing methods for an optical data recording mediumaccording to the present invention provide a cavity corresponding to thedesired shape of the protrusion in a die, and then introduce moltenresin to the mold and apply pressure in an injection molding process.This produces a substrate with a signal pattern transferred from thestamper in the mold and a protrusion simultaneously formed to thesubstrate surface, thereby improving mass production of the optical datarecording medium.

In another aspect of a manufacturing method for a disc-shaped opticaldata recording medium having a signal recording layer for reading and/orwriting data using light, a 10 μm to 200 μm thick transparent protectivelayer disposed over the signal recording layer, and a protrusionprojecting from the surface of the transparent protective layer on thelight-incidence surface side to which light is emitted to the signalrecording layer, the protrusion is formed on the optical data recordingmedium by bonding thereto a part in the shape of the protrusion.

By thus bonding parts forming the desired shape of the protrusion to thedisc surface, this optical data recording medium manufacturing methodcan easily form the protrusion at a desired location on the disc,thereby improving mass production.

In another aspect of a manufacturing method for a disc-shaped opticaldata recording medium having a signal recording layer for reading and/orwriting data using light, a 10 μm to 200 μm thick transparent protectivelayer disposed over the signal recording layer, and a protrusionprojecting from the surface of the transparent protective layer on thelight-incidence surface side to which light is emitted to the signalrecording layer, the protrusion is formed on the optical data recordingmedium by dripping a liquid material onto the optical data recordingmedium and curing the liquid material in the shape of the protrusion.

This manufacturing method can easily produce protrusions of the desiredshape at the desired location of the disc surface by simply changing howthe liquid material is dripped onto the substrate. Little time is alsoneeded to form the protrusions, and optical data recording media havingprotrusions according to the present invention can therefore bemanufactured at low cost.

In another aspect of a manufacturing method for a disc-shaped opticaldata recording medium having a signal recording layer for reading and/orwriting data using light, a 10 μm to 200 μm thick transparent protectivelayer disposed over the signal recording layer, and a protrusionprojecting from the surface of the transparent protective layer on thelight-incidence surface side to which light is emitted to the signalrecording layer, the protrusion is formed on the optical data recordingmedium by a screen printing process using a screen having the desiredshape of the protrusion.

This manufacturing method can easily produce protrusions of the desiredshape at the desired location of the disc surface by simply changing thepattern of the protrusions in the screen. Little time is thereforeneeded to form the protrusions, and optical data recording media havingprotrusions according to the present invention can therefore bemanufactured at low cost.

The material used to make the parts bonded to the optical data recordingmedium surface, and the material of the protrusions formed by screenprinting, in the optical data recording medium manufacturing methodsdescribed above is preferably a resin. This makes materials handlingsimple, enables using low cost materials, and improved productivity. Theresin is further preferably a UV-cure resin, a thermosetting resin, or apressure-sensitive adhesive. Each of these materials is inexpensive andeasily procured.

Further preferably, the protrusion is disposed in an area between thecenter hole and a clamping area where the optical data recording mediumis held for reading and/or writing data in the signal recording layer.

This configuration locates the protrusion on the optical data recordingmedium surface on the inside circumference side of the clamping area.The protrusion therefore does not interfere (collide) with the opticalhead, and the transparent protective layer will not be scratched whenthe disc is placed on a flat surface with the transparent protectivelayer facing said flat surface because the protrusion disposed to thesame side of the disc prevents the transparent protective layer fromtouching the flat surface. Disc reliability can therefore be assured fora long time.

Yet further preferably, the protrusion is disposed in an area betweenthe clamping area for holding the optical data recording medium whenreading or recording data in the signal recording layer, and the signalarea for recording or reading data in the signal recording layer.

Yet further preferably, the protrusion is disposed to an area within 2mm to the outside in the radial direction from the outside circumferenceedge of the clamping area. In this case the optical data recordingmedium assures no interference between the protrusion and optical headregardless of the recording and playback device in which it is used.

Yet further preferably, the protrusion is disposed in the clamping areafor holding the optical data recording medium when reading or recordingdata in the signal recording layer.

Because the disc in this case is clamped on both sides of theprotrusion, the protrusion is prevented from interfering with theoptical head while also protecting the transparent protective layer.Greater clamping force can also be applied to the optical data recordingmedium.

Yet further preferably, the protrusion is formed to a height of 0.05 mmto 0.5 mm from the surface of the transparent protective layer. Becausethe protrusion thus projects sufficiently from the transparentprotective layer surface with this configuration, the transparentprotective layer will not be scratched when the disc is placed on a flatsurface because the transparent protective layer is prevented fromtouching said flat surface by the protrusion. A more dependable opticaldata recording medium can therefore be manufactured.

Scratch-prevention and cost are further improved if the protrusionheight is further preferably 0.1 mm to 0.3 mm from the surface of thetransparent protective layer.

Another aspect of the present invention is a clamping method for adisc-shaped optical data recording medium having a signal recordinglayer for reading and/or writing data by emitting light using an opticalhead with a 0.7 to 0.9 numeric aperture, and a 10 μm to 200 μm thicktransparent protective layer disposed over the signal recording layer.The optical data recording medium has a clamping area on the outside ofthe center hole in the radial direction for holding the optical datarecording medium when reading or recording data in the signal recordinglayer, a signal area on the outside of the clamping area in the radialdirection for recording or reading data in the signal recording layer,and a protrusion projecting from the surface of the transparentprotective layer in the clamping area on the light-incidence side of thesignal recording layer to which light is emitted for reading and/orwriting information. The clamping method holds the optical datarecording medium on both sides of the protrusion when recording orreading data in the signal recording layer of the optical data recordingmedium.

By holding the optical data recording medium on both sides of theprotrusion, this disc clamping method can apply greater clamping force,the disc can be spun stably, and good signal quality can be achieved.

Preferably, the area for clamping on both sides of the protrusion on thelight incidence side is in a radial area with a radius of 11 mm to 16.5mm.

Yet further preferably, the optical data recording medium is clamped byboth holding the optical data recording medium on both sides of theprotrusion on the light incidence side and holding the protrusion.

By thus clamping the disc in two areas on opposite sides of theprotrusion and by applying pressure directly to the protrusion, evengreater clamping force can be applied.

With an optical data recording medium according to the present inventionthe protrusion will not interfere (collide) with the optical head andthe transparent protective layer is protected from scratches when thedisc is placed transparent protective layer-side down on a flat surfacebecause the protrusion prevents the transparent protective layer fromtouching the flat surface.

Furthermore, the load on the rotating spindle (motor) caused by a weightimbalance in the protrusion is also reduced because the protrusion islocated near the center spindle hole.

The clamping method of an optical data recording medium according to thepresent invention holds the optical data recording medium in a clampingarea on either or both sides of the protrusion. The optical datarecording medium can therefore be held and spun stably during recordingand playback, assuring consistent recording and playback and good signalquality.

The optical data recording medium manufacturing method of this inventioncan also easily form the protrusion, thus improving optical datarecording medium productivity.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become readily understood from the followingdescription of preferred embodiments thereof made with reference to theaccompanying drawings, in which like parts are designated by likereference numeral, and in which:

FIG. 1A is a section view of an optical data recording medium having aprotrusion according to a first embodiment of the present invention, andFIG. 1B is a plan view of the same disc;

FIG. 2A to FIG. 2E are partial section views of possible protrusionshapes;

FIG. 3A to FIG. 3C show various configurations of the protrusion whenseen in plan view from above the protrusion;

FIG. 4 is a section view of another optical data recording medium inwhich the configuration of the area from the spindle hole to theclamping area differs from that shown in FIGS. 1A and 1B;

FIG. 5A to FIG. 5C are section views of a first method of manufacturingan optical data recording medium having a protrusion according to thepresent invention;

FIG. 6 shows a second method of manufacturing an optical data recordingmedium having a protrusion according to the present invention;

FIG. 7A and FIG. 7B show a third method of manufacturing an optical datarecording medium having a protrusion according to the present invention;

FIG. 8A is a partial section view of an optical data recording mediumhaving a protrusion according to a second embodiment of the presentinvention, and FIG. 8B is a partial plan view of the same optical disc;

FIG. 9 is a partial section view showing reading and/or writing data tothe data recording layer of an optical data recording medium having aprotrusion according to a second embodiment of the invention;

FIG. 10 shows an example of a method of forming the protrusion in amethod for manufacturing an optical data recording medium according tothe second embodiment of the invention;

FIG. 11A to FIG. 11C are schematic section views showing methods ofclamping an optical data recording medium having a protrusion accordingto a third embodiment of the invention;

FIG. 12A to FIG. 12C are partial section views of chucking the opticaldata recording medium for reading and/or writing data to the datarecording layer;

FIG. 13 is a partial section view showing a warped optical datarecording medium placed on a flat surface;

FIG. 14A and FIG. 14B show examples of an optical data recording mediumhaving a difference in the surface elevation of the transparentprotective layer and the clamping area CA;

FIG. 15 is a partial section view showing an optical data recordingmedium having a smaller protrusion; and

FIG. 16 is a partial section view showing the optical data recordingmedium of the third embodiment when clamped from both top and bottomsides of the disc.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to the accompanying figures.

Embodiment 1

FIG. 1A is a side section view of a preferred embodiment of an opticaldata recording medium according to the present invention. The opticaldata recording medium 110 (also referred to below as simply “disc”)shown in FIG. 1A has a protrusion 100 disposed on the surface thereofbetween the inside circumference side of the clamping area CA and theoutside edge of the spindle hole 101. FIG. 1A is a section view of thisoptical data recording medium 110, and FIG. 1B is a top plan view of theoptical data recording medium 110.

The outside diameter of this optical data recording medium 110 is 120mm. The clamping area CA is the area where the optical data recordingmedium 110 is clamped and held when reading and/or writing data to thesignal recording layer 103. The inside diameter D_(CAI) of the clampingarea CA is 22 mm and the outside diameter D_(CAO) is 33 mm.

A transparent protective layer 102 protects the signal recording layer103. A light beam with a 405 nm wavelength, for example, is emitted froman optical head through the transparent protective layer 102 and focusedon the signal recording layer 103 for reading and/or writing data.

The transparent protective layer 102 is, for example, 100 μm thick. Thesignal recording layer 103 is formed over signal pits or grooves thatare formed in the signal area SA of the signal substrate 104. The insidediameter D_(SAI) of the signal area SA is 42 mm and the outside diameterD_(SAO) is 119 mm. The signal recording layer 103 could be a multilayerfilm including a GeSbTe phase-change film, a multilayer film including apigment film, or a metal alloy thin film.

The diameter Dc of the spindle hole 101 is 15 mm. The inside diameterD_(ti) of the protrusion 100 is 18 mm, the width in the radial direction(radial width) is 1 mm, and the height of the protrusion 100 above thesurface of transparent protective layer 102 is 0.3 mm. The radial widthof the protrusion 100 is preferably 0.2 mm to 1 mm. A width of 0.2 mm orgreater is preferred to assure sufficient mechanical strength.

The height of the protrusion 100 from the surface of transparentprotective layer 102 is preferably 0.1 mm to 0.5 mm. If the height ofthe protrusion 100 is at least 0.1 mm above the surface of thetransparent protective layer 102 and the transparent protective layer102 is placed on a flat surface with the protrusion 100 facing down, thetransparent protective layer 102 will not contact the flat surface andwill be protected from scratching.

Furthermore, while the inside diameter D_(ti) of the protrusion 100 is18 mm, the inside edge of the protrusion 100 must only be separated atleast 0.1 mm from the outside edge of the spindle hole 101. In otherwords, the inside diameter of protrusion 100 must be greater thandiameter (D_(C)+0.2) mm and the outside diameter must be less thaninside diameter D_(CAI) of the clamping area CA. If inside diameterD_(ti) is greater than (D_(C)+0.2) mm, the disc can be stably clampedand spun, assuring good signal quality, during recording and playbackwithout interference between the centering cone of the recorder orplayback device and the protrusion 100.

Table 1 shows the effect of the protrusion 100 at different elevationsfrom the surface of the transparent protective layer 102. The indicesused to evaluate the effectiveness of the protrusion 100 were the amountof scratching on the surface of the transparent protective layer 102,and the ease with which the disc 110 can be picked up, when placed withthe transparent protective layer 102 face down against a flat surface.TABLE 1 Protrusion height and effect Height (mm) of 0 0.05 0.1 0.2 0.30.4 0.5 protrusion from transparent protective layer surface Surfacescratching NG Some OK OK OK OK None Ease of pickup NG Poor Poor GoodGood Very Very good good

When the height of the protrusion 100 is 0 mm from the surface of thetransparent protective layer 102, that is, when there is no protrusion100, there is excessive scratching of the transparent protective layerand it is difficult to pick the disc up off a flat surface. While aprotrusion height of only 0.05 mm provides a slight improvement inscratching and ease of picking up the disc, the protective margin isstill not sufficient and the surface of the transparent protective layermust be treated in some way, such as by hardening, to improve scratchresistance.

A protrusion height of 0.1 mm provides a significant improvement inscratching, that is, there is substantially no scratching. When theprotrusion height is 0.2 mm to 0.3 mm there is essentially no scratchingof the transparent protective layer and the disc is easy to pick up.

When the protrusion height is 0.4 mm there is essentially no scratchingof the transparent protective layer and the disc is very easy to pickup. With a protrusion height of 0.5 mm no scratches were found in thetransparent protective layer surface and the disc was very easy to pickup.

Increasing the height of the protrusion 100 to greater than 0.5 mm abovethe surface of the transparent protective layer does not yield anyimprovement in scratch protection or ease of picking the disc up.Furthermore, a height greater than 0.5 mm increases the amount andtherefore the cost of the required materials, and is therefore notdesirable.

It should be noted that if the diameter D_(C) of spindle hole 101 isapproximately 15 mm, the diameter of the protrusion 100 is between 17.5mm to 22 mm, and the height of the protrusion 100 from the surface oftransparent protective layer 102 is 0.3 mm or less, the three benefitsdescribed below, which include the effects noted above, can be achieved.(Note that (2) and (3) below are the effects described above.)

(1) The protrusion 100 does not interfere with the chuck used to clampthe disc during recording and playback of the optical disc.

(2) Scratches in the transparent protective layer 102 can be preventedwhether the disc is warped or placed on a flat surface.

(3) The disc can be easily picked up from a flat surface even if thedisc is warped.

Item (1) above is described first. FIG. 12A to FIG. 12C show chuckingthe optical data recording medium for recording or playing the disc.FIGS. 12A-12C show a simple, common chucking method such as used withDVD and other media. As shown in FIG. 12A the optical data recordingmedium 110 is loaded above the chuck 1200. The jaws 1201 of the chuckare extended outward by a spring 1202. If the diameter D_(C) of spindlehole 101 in optical data recording medium 110 is 15 mm, the jaws 1201have an outside diameter DH of approximately 17 mm to ensure that thecircumference of the spindle hole 101 is firmly chucked. A diameter DHof 17 mm also assures sufficient mechanical strength in the jaws 1201.

As shown in FIG. 12B, the optical data recording medium 110 and the jaws1201 touch. If the protrusion 100 is disposed to an area outside the17.5 mm or greater diameter area at the disc center, the protrusion 100will be beyond the reach of the jaws 1201. There will therefore be nocontact between the protrusion 100 and jaws 1201, and no load will beapplied to the protrusion 100 and jaws 1201. When pressure is thenapplied to the top of the disc so as to push it downward, the springs1202 are forced to contract and the jaws 1201 move inward toward thecenter of the chuck 1200 until the jaws 1201 pass through the spindlehole 101 of the disc. The springs 1202 then expand outward, pushing thejaws 1201 out.

This results in the optical data recording medium 110 being clamped bythe chuck 1200 as shown in FIG. 12C. As shown in FIGS. 1A and 1B, theinside diameter D_(CAI) of the clamping area CA is 22 mm. The chuck 1200therefore holds the disc 110 in the area outside this inside diameterD_(CAI), but there is no interference between the protrusion 100 andchucking surface 1203 because the outside diameter of protrusion 100 isless than 22 mm.

Furthermore, because the inside diameter of the clamping area in aconventional optical disc such as DVD media is also 22 mm, interferencebetween the protrusion 100 and the jaws and chucking surface of thechuck can be prevented even if the optical data recording medium 110 isaccidentally chucked using a chuck for conventional DVD media.

If the protrusion 100 is located in a circumferential band with a 17.5mm inside diameter and 22 mm outside diameter when the diameter D_(C) ofthe spindle hole 101 is approximately 15 mm, it is therefore possible toavoid interference between the protrusion 100 and chuck 1200, includingthe jaws 1201, even when using a simple chuck 1200 of the type thatapplies the greatest chucking force to the optical data recording medium110.

Items (2) and (3) are described above with reference to Table 1, and aredescribed in further detail below with reference to FIG. 13. If thethickness of the transparent protective layer 102 is 100 μm, the maximumdeflection allowed in the optical data recording medium 110 is 0.35degree. This is because if disc warpage exceeds 0.35 degree the errorrate during recording and playback rises to a level at which errorcorrection is not possible.

FIG. 13 shows an optical data recording medium 110 with the maximumallowable warpage of 0.35 degree when placed on flat surface P with thetransparent protective layer 102 facing surface P. The optical datarecording medium 110 generally warps on the outside circumference sideof the clamping area CA (that is, outside the 33 mm diameter center areaof the disc). If the optical data recording medium 110 in this case hasthe protrusion 100 disposed in the circumferential region with a 17.5 mminside diameter and 22 mm outside diameter, and the height of theprotrusion 100 from the surface of the transparent protective layer 102is 0.3 mm, there is no contact between the outside edge E of the opticaldata recording medium 110 and surface P. That is, because the outsidediameter of optical data recording medium 110 is 120 mm,(60−33/2)*TAN(0.35 deg)=0.27 mm. The optical data recording medium 110is therefore this much closer to the surface P, but if the top of theprotrusion 100 is 0.3 mm above the surface of transparent protectivelayer 102, outside edge E will not touch surface P.

When someone then attempts to pick up the disc 110, the increasedcontact area between the fingers and the outside edge E of the disc 110makes it easier to pick the disc 110 up.

The surface of the transparent protective layer 102 is also protectedfrom scratches due to contact with the surface P because it does nottouch the surface P.

The height of the protrusion 100 above the surface of the transparentprotective layer 102 can be determined according to the warpage allowedin the optical data recording medium 110. When the maximum allowedwarpage in the optical data recording medium 110 is 0.35 degree as inthis example, however, a protrusion height of 0.3 mm or less above thesurface of the transparent protective layer 102 is sufficient to achievethe benefits described above.

FIG. 14A and FIG. 14B show an alternative case in which there is adifference between the surface elevation of transparent protective layer102 and the surface elevation of the clamping area CA. FIG. 14A shows anexample of an optical data recording medium in which the surface of thetransparent protective layer 102 is recessed 25 μm from the surface ofclamping area CA so that the transparent protective layer 102 is fartherfrom the recording/playback head than the clamping area CA. FIG. 14Bshows a different example in which the surface of the clamping area CAis recessed 25 μm from the surface of clamping area CA so that thesurface of the clamping area CA is farther from the recording/playbackhead.

To assure that the height of protrusion 1400 from the surface of thetransparent protective layer 102 is 0.3 mm or less as shown in FIGS.12A-12C, the height of the protrusion 1400 from the surface of theclamping area CA is controlled to 0.275 mm or less in the case shown inFIG. 14A. To likewise assure that the height of protrusion 1400 from thesurface of the transparent protective layer 102 is 0.3 mm or less in thecase shown in FIG. 14B, the height of protrusion 1400 from the surfaceof the clamping area CA is controlled to 0.325 mm or less. This assuresin both cases that the height of the protrusion 1400 from the surface ofthe transparent protective layer 102 is 0.3 mm or less.

Furthermore, to prevent interference of the protrusion 1400 with thechucking surface 1203 and chuck 1200 better than the example shown inFIGS. 12A-12C, the protrusion 1400 can be disposed in a circumferentialarea having a 17.5 mm inside diameter and 21 mm outside diameter asshown in FIG. 15. If inside diameter D_(CAI) is 22 mm in this case a gapof 0.5 mm in the radial direction is achieved between the protrusion andthe clamping area CA.

Furthermore, if the disc is not greatly warped as shown in FIG. 13, theheight of the protrusion 1400 from the surface of the clamping area CAcan be 0.2 mm or less regardless of whether or not there is a stepbetween the transparent protective layer surface and the clamping area.This still avoids interference between the protrusion 1400 and chuckingsurface 1203 and chuck 1200, enables the depth G of the chuck 1200 to bereduced to a shallow 0.25 mm, and provides greater freedom of design inthe chuck 1200.

FIGS. 2A-2E show various examples of the sectional shape of theprotrusion. As shown in FIGS. 2A-2E, the protrusion could be square(rectangular) 201, trapezoidal 202, elliptical 203, semi-circular 204,or triangular 205. It will also be obvious that the shape of thisprotrusion shall not be limited to shapes such as shown in FIGS. 2A-2E,and any shape whereby the protrusion projections above the surface ofthe transparent protective layer can be used.

Examples of the shape of the protrusion when seen in a top view areshown in FIGS. 3A-3C. FIG. 3A shows a rectangular configuration, FIG. 3Bshows a configuration having multiple discrete protrusions, and FIG. 3Cshows a broken ring configuration. With the configuration shown in FIG.3B there are four discrete dot-like protrusions 302 disposed at 90degree intervals in the circumferential direction.

The broken ring configuration shown in FIG. 3C has three arc-shapedprotrusions 303 disposed at 120 degree intervals in the circumferentialdirection on the same circular path.

When multiple discrete protrusions are disposed with a configurationsuch as shown in FIG. 3B or FIG. 3C, the number of protrusions shall notbe so limited.

Furthermore, the shape of the protrusion(s) when seen in plan view shallnot be limited to those shown in FIGS. 3A-3C. More specifically, theprotrusion(s) can be shaped as desired insofar as they project out fromthe surface of the transparent protective layer and are located in acircumferential region with an inside diameter of (D_(C)+0.2) mm and anoutside diameter of D_(CAI).

FIG. 4 shows an example of an optical data recording medium 410 in whichthe configuration from the spindle hole to the clamping area differsfrom the configuration shown in FIGS. 1A and 1B. This disc differs fromthat shown in FIGS. 1A and 1B in that the transparent protective layer402 also covers the clamping area CA but is absent around the spindlehole 401. The inside diameter D_(CV) of the transparent protective layer402 is therefore D_(CV)<=D_(CAI). The protrusion 400 is located betweenthe spindle hole 401 and the inside diameter of clamping area CA. Thetotal height T_(t) of the protrusion 400 isT _(t) =T _(tcv)+(transparent protective layer thickness)where T_(tcv) is the height above the surface of the transparentprotective layer 402. In this example T_(tcv) is 0.1 mm to 0.5 mm.

It is also possible for the transparent protective layer to not beformed in the clamping area CA.

The effect of disposing a protrusion projecting from the surface of thetransparent protective layer on the light incidence side of the areabetween the spindle hole and clamping area of the optical data recordingmedium is described next.

The protrusions cannot be disposed to any desired place on the opticaldisc, and more specifically must be disposed where there will be nocontact between the protrusions and the optical head. With the opticaldata recording medium according to a first embodiment of the inventionthe protrusions are disposed in the area between the spindle hole andclamping area CA. When reading and/or writing data to the signalrecording layer the optical head is always on the outside circumferenceside of the clamping area CA. As a result, there is no contact betweenthe optical head and the protrusions, which are on the insidecircumference side of the clamping area CA and separated from theoptical head by the clamping area CA.

A method of manufacturing these protrusions according to the presentinvention is shown in FIGS. 5A-5C using by way of example an injectionmolding process.

A pair of dies 500 is prepared and a stamper 501 is set in one die asshown in FIG. 5A. This stamper 501 contains signal 517. The side of thedies 500 holding the stamper 501 also has cavities 502. These cavities502 are formed to the desired shape of the protrusion.

The mold 500 is then closed as shown in FIG. 5B and molten resin 510 isinjected. The molten resin 510 thus penetrates the signal 517 patternand the cavities 502. The mold is then cooled and spindle hole 511 isstamped as shown in FIG. 5C to obtain a signal substrate 516 with signal517 formed in the surface thereof. A signal recording layer is thenformed over the signal 517 surface, and a transparent protective layeris formed as shown in FIG. 4. A transparent protective layer is formedfrom above the protrusion 515 to produce an optical data recordingmedium 110 as shown in FIGS. 1A and 1B. Because the transparentprotective layer also accumulates on the protrusion 515, a protrusionwith the same shape is also formed in the transparent protective layer.

FIG. 6 shows a method in which parts having the desired shape of theprotrusion are fixed to the disc surface with adhesive. In this case thedesirably shaped protrusions 600 are bonded to the flat surface of theoptical data recording medium 601, that is, a disc having no surfaceprotrusions. A pressure-sensitive adhesive, UV-cured resin, orthermosetting resin, for example, could be used. The material used forthe protrusions 600 is preferably lightweight, easy to handle, and lowcost, and resin is therefore suitable.

The material for bonding the protrusions 600 can be precoated to thepart of the protrusions 600 that will touch the protrusion-less disc601. Alternatively, the part touching the protrusion-less disc 601 couldbe heated and melted for bonding. The protrusions 600 could even bemetal. Using the method shown in FIG. 6, a flat optical data recordingmedium 601 having no protrusions could be manufactured in one process,parts forming the protrusions can be produced in a separate process tothe desired shapes, and protrusions with a particular desired shapecould then be bonded to the disc surface. This method offers wide designlatitude.

FIGS. 7A and 7B show a method in which drops of liquid resin aredeposited and cured on the disc surface. As shown in FIG. 7A liquidresin 700 is dripped from a nozzle 701 to the desired locations on theprotrusion-less disc 601. The protrusion-less disc 601 can rotated ormoved, or the nozzle 701 could be moved, while dripping the resin. Theliquid resin 700 in this case is preferably a UV-cured resin orthermosetting resin. Thus dripping and then curing the resin results inprotrusions 715 of a desired configuration as shown in FIG. 7B. Using adisc such as shown in FIG. 4, the resin is dripped onto the signalsubstrate.

Protrusions can also be formed from a liquid resin using a screenprinting process. In this case a printing screen is formed with thedesired shape of the protrusions, and the liquid resin is screen-printedonto the disc surface. Because the method shown in FIGS. 7A and 7B doesnot require preparing and handling discrete protrusion parts, it canform the protrusions more economically than the process shown in FIG. 6.

As described above, an optical data recording medium according to thisfirst embodiment of the invention has one or more protrusions located onthe surface between the inside circumference of the clamping area CA andthe outside edge of the spindle hole, assuring that the protrusions willnot contact the optical head during recording or playback.

Furthermore, surface scratches can be prevented even when the disc isplaced on a flat surface with the transparent protective layer sidefacing down because the protrusions assure that the transparentprotective layer is sufficiently above and does not contact the flatsurface.

Yet further, the proximity of the protrusions to the spindle holeminimizes the effect of any weight imbalance in the protrusion part. Astable, high quality signal can therefore be achieved.

Embodiment 2

FIGS. 8A and 8B show an optical data recording medium 810 having aprotrusion 800 disposed in the area between the clamping area CA andsignal area SA. FIG. 8A is a section view and FIG. 8B is a plan viewfrom the transparent protective layer 802 side of the disc. The insidediameter and outside diameter of the clamping area CA and signal area SAare the same as in the first embodiment. The thickness of thetransparent protective layer 802 is also the same as in the firstembodiment. In this example the inside diameter D_(ti) of protrusion 800is 33 mm (=D_(CAO)), and the outside diameter D_(to) is 35 mm. Theheight T_(tcv) of the protrusion 800 is 0.25 mm. The protrusion 800 isformed on the surface of signal substrate 804.

FIG. 9 is a partial section view when reading and/or writing the opticaldisc.

When recording or playing a high density optical disc with a 0.1 mmthick transparent protective layer on the laser incidence side (theread/write side) of the disc using a 0.7 to 0.9 NA optical head, such asa high 0.85 NA optical head, the distance between the optical head andthe high density optical disc, known as the working distance WD, isgenerally very small, typically 0.1 to 0.4 mm. A working distance WD of0.4 mm or less is recommended, for example, in ISO M 2002 TechnicalDigest ThB.1 published by the International Symposium on Optical Memory.

Because of the short working distance WD in this case, the optical headcan easily strike the transparent protective layer of the disc when thefocusing servo is disrupted by such external factors as vibration of thedisc surface. The high NA used with high density optical discs meansthat dust on the surface of the transparent protective layer can easilydisrupt the focusing servo. When the focusing servo is off track, theoptical head can easily collide with the protrusion on the disc surface.To prevent this, a shield for protecting the lens is required on thesurface of the optical head. The thickness of this shield (approximately0.1 mm) further decreases the working distance to 0.3 mm or less. If theworking distance of the optical head increases, the outside diameter ofthe lens also increases. The outside diameter f of a lens with a 0.4 mmworking distance is 6 mm to 8 mm (including the lens holder).

When reading and/or writing the signal area with inside diameter D_(SAI)as shown in FIG. 9, the lens holder 900 intrudes on the area betweenclamping area CA and signal area SA by an amount equal to the radius Rpart of the lens holder 900. With a 0.85 NA, for example, the actualworking distance WD of the lens is a narrow 0.2 mm to 0.3 mm. That is,with an optical data recording medium as shown in FIGS. 8A and 8B, theoptimal height T_(tcv) of the protrusion will differ according to thelocation of the protrusion.

The height T_(tcv) of this protrusion 800 is considered next.

The closer protrusion 800 gets to inside diameter D_(SAI), the closerprotrusion 800 gets to the lens holder 900. The height T_(tcv) musttherefore be lowered. Furthermore, because the outside diameter D_(to)of protrusion 800 is 35 mm, there is 3.5 mm to inside diameter D_(SAI)(=42 mm). If the actual working distance WD of the lens is 0.2 mm, thereis 0.5 mm of space between the lens holder 900 and protrusion 800because the radius R of the lens holder is approximately 3 mm. Radius Ris approximately 4 mm if the working distance WD is 0.3 mm, but becauseheight T_(tcv) is 0.25 mm, the protrusion 800 will not collide with thelens holder 900.

It is thus necessary to consider the working distance WD of the lenswhen the protrusion is located in the area between clamping area CA andsignal area SA. However, if the height T_(tcv) of the protrusion is 0.1m to 0.3 mm, the protrusion 800 will not collide with the lens holder900.

It will also be obvious that the surface protection performance of thetransparent protective layer is also achieved.

It should be noted that the protrusion can be located in the areabetween the clamping area CA and signal area SA as described in thissecond embodiment of the invention whether the transparent protectivelayer is not formed in the clamping area CA as shown in FIGS. 8A and 8B,or whether the area of the transparent protective layer is disposed toan area as shown in FIGS. 1A and 1B or FIG. 4.

The protrusion in this second embodiment can also be manufactured usingthe same materials and methods described in the first embodiment. Notethat depending upon the inside diameter of the stamper, it may benecessary to provide a cavity in the stamper with the injection moldingmethod shown in FIG. 5. For example, if the inside diameter of thestamper is less than 33 mm, the stamper thickness could be increased anda cavity of desirable depth and configuration formed in the stamper byetching or machining. As shown in FIG. 10, a protrusion 1001 can beformed on the signal substrate and the transparent protective layer 1010formed thereon to form the surface protrusion 1000. The protrusion canalso be formed on an optical data recording medium as shown in FIGS. 8Aand 8B by a molding process such as shown in FIGS. 5A-5C.

The shape and configuration of the protrusion can be the same asdescribed in the first embodiment above. When the protrusion is in anarea between the clamping area CA and signal area SA as described inthis second embodiment of the invention, and particularly when theprotrusion is within 2 mm on the outside circumference side of theclamping area CA, collision of the optical head with the protrusion canbe prevented during both recording and playback, and surface scratchescan be prevented even when the optical data recording medium is placedon a flat surface with the transparent protective layer of the discfacing the flat surface because the protrusion assures that the surfaceof the disc does not contact the surface on which it is placed.

Embodiment 3

An optical data recording medium in which the protrusion is located inthe clamping area CA is shown in FIGS. 11A-11C as a third embodiment ofthe present invention. FIG. 11A is a section view of the disc.

The inside diameter D_(ti) and outside diameter D_(to) of the protrusion1100 are defined by the following relation.D _(CAI) <=D _(ti) <D _(to) <=D _(CAO)

This configuration also prevents scratching when the optical datarecording medium 1110 is placed on a flat surface with the transparentprotective layer 1102 facing the flat surface because the protrusionassures a sufficient gap between the transparent protective layer 1102and said flat surface.

Collision of the optical head with the protrusion is also preventedbecause the optical head does not enter the clamping area CA.

Note that the thickness of the transparent protective layer, insidediameter D_(CAI), and outside diameter D_(CAO) are the same in thisembodiment as in the first embodiment.

The width of the protrusion 1100 and the height of the protrusion fromthe surface of the transparent protective layer 1102 are also the sameas in the first embodiment, that is, in the ranges 0.2 mm to 1 mm, and0.1 mm to 0.5 mm, respectively.

Unlike in the first and second embodiments, the disc drive clamps theoptical data recording medium 1110 on both sides of the protrusion 1100in this third embodiment. This is possible except when D_(CAI)=D_(ti) orD_(to)=D_(CAO). FIG. 11B and FIG. 11C show two different ways ofclamping the optical data recording medium 1110 on both sides of theprotrusion 1100.

In the example shown in FIG. 11B, the clamp 1120 applies pressure to thedisc in the clamping area on both sides of the protrusion 1100. The disccan be held with sufficient force in this case despite the protrusion1100 because the clamping member has a channel providing clearance forthe protrusion 1100.

In the example shown in FIG. 11C, the clamp 1130 applies pressure to thedisc in the clamping area on both sides of the protrusion 1100, and alsoapplies pressure to the protrusion 1100. This method provides even morepositive clamping of the disc because pressure is applied to a largerarea of the disc than with the method shown in FIG. 11B.

The optical data recording medium can be held stable and rotated withsufficient pressure during both recording and playback to assure goodsignal quality and reliable recording and playback performance.

It should be noted that the disc is clamped on both sides of theprotrusion 1100 in this embodiment, but it could be held only in thearea between inside diameter D_(CAI) and the inside circumference edgeof the protrusion 1100, or the area between outside diameter D_(CAO) andthe outside circumference edge of the protrusion 1100.

While this third embodiment has been described with reference to theconfiguration shown in FIGS. 11A-11C, it could be configured as shown inFIG. 4 and FIG. 8. That is, this protrusion could be used on a disc inwhich the transparent protective layer is not formed in the clampingarea CA, or on a disc in which the transparent protective layer is notin the clamping area CA and there is a step between the surfaceelevations of the signal substrate and the transparent protective layer.

The protrusion 1100 of this third embodiment can also be formed usingthe same materials and methods described in the first and secondembodiments above.

The shape and configuration of the protrusion could also be as describedin the first embodiment.

Clamping an optical data recording medium according to the presentinvention shall not be limited to holding the disc with chucking jaws inthe clamping area CA on only one side of the disc as shown in FIG. 12Ato FIG. 12C and FIG. 15. More specifically, the optical data recordingmedium could be clamped from both sides of the disc. This is shown inFIG. 16, a section view of the optical data recording medium 1600 beingclamped in the clamping area CA from above and below the disc by meansof a top clamp 1605 and a bottom clamp 1606. In this example theprotrusion 1601 is disposed in the clamping area CA, and the area onboth sides of the protrusion 1601 is supported by bottom clamp 1606 onthe laser-incidence side of the disc.

The material used to manufacture the signal substrate is notparticularly discussed in the above-described embodiments, but ispreferably a plastic such as polycarbonate, norbornene resin, orpolyolefin resin.

The transparent protective layer can also be formed by applying a sheetfilm thinner than the desired thickness with adhesive, or applying acoat of liquid resin. When a thin sheet film is applied with adhesive,the adhesive could be a UV-cure resin, thermosetting resin, or pressuresensitive adhesive, for example.

When a coat of liquid resin is applied, the resin could be a UV-cureresin or thermosetting resin, for example.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbe apparent to those skilled in the art. Such changes and modificationsare to be understood as included within the scope of the presentinvention as defined by the appended claims, unless they departtherefrom.

1. An optical disc with a center hole, the optical disc comprising: asignal substrate; a signal recording layer for storing data; atransparent protective layer having a 10 μm to 200 μm thickness disposedover said signal recording layer; and a protrusion projecting from asurface of said transparent protective layer, wherein a signal area ofthe optical disc is located over said signal recording layer, a clampingarea of the optical disc is located between the signal area and thecenter hole, and said protrusion is disposed at an area of the opticaldisc between the center hole and the clamping area, wherein the centerhole has a 15 mm diameter, the optical disc has a 120 mm outsidediameter, and the clamping area is located between a 22 mm diameter anda 33 mm diameter.
 2. An optical disc according to claim 1, wherein theprotrusion is disposed at least 0.1 mm in a radial direction from anoutside edge of the center hole.
 3. An optical disc according to claim2, wherein the protrusion is disposed to the area between a 17.5 mminside diameter and 22.0 mm outside diameter.
 4. A playback device forplayback of the information from the optical disc according to claim 1,wherein the optical disc is clamped on the clamping area, and theoptical disc is rotated during playback, wherein the data transfer rateduring playback is higher than the Digital Versatile Discs media.
 5. Arecording device for recording the information onto the optical discaccording to claim 1, wherein the optical disc is clamped on theclamping area, and the optical disc is rotated during recording, whereinthe data transfer rate during recording is higher than the DigitalVersatile Discs media.